changed from dateTime to duration

lib/model/requests/create_relative_time_alarm_request.dart

@@ -3,7 +3,7 @@ import '../alarm/relative_time_alarm.dart';
 import 'create_alarm_request.dart';
 
 class CreateRelativeTimeAlarmRequest extends CreateAlarmRequest {
-  final DateTime? triggerAt;
+  final Duration? triggerAt;
 
   const CreateRelativeTimeAlarmRequest({this.triggerAt})
     : super(alarmType: AlarmType.timeRelative);